


In Heat

by orphan_account



Category: Undertale (Video Game)
Genre: (hopefully not), (that would be weird), Anal Sex, Ecto-Penis, Ecto-Tongue, F/M, NO plot not even a little bit, Oral Sex, PWP, Reader has female parts, Soul Sex, Tentacles, Vaginal Sex, desperate sans, every type of sex okay, im sorry, ive sinned so bad i cant come back from this, pillow humping, reader is female, sans using his magic in ways toby fox never imagined, sans whining a lot, tentacle fucking
Language: English
Status: Completed
Published: 2016-05-15
Updated: 2016-05-15
Packaged: 2018-06-08 12:51:10
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 2
Words: 1,824
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6855421
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: <blockquote class="userstuff">
              <p>sans is in heat. That's it, there's no plot, it's just good ol' skele-sin, and reader gets caught in it</p>
            </blockquote>





	1. all alone

**Author's Note:**

> I guess this is some sort of AU, you've lived with sans for a while but not long enough to see him in heat. There's no plot leave me alone I just wanna write sans in heat and also a reader insert im gross asgdghfjkglh

Sans wakes up, sweating, his bones shaking with magic and his soul aching. "so it begins," he mutters, groaning as he rolls over in bed. Already his head is throbbing. He needs, he needs... you. But he isn't selfish enough to go straight to you. Besides, he'd just... scare you off with his intensity. He drags a hand down his face and gently ruts into the pillow next to him, groaning. He hates doing this, but at least it's something. Plus, Papyrus should be gone for work already, so he's alone. Quite unfortunate that you work on Saturdays...

He gets up and quickly lifts his shirt off, straddling the pillow. His soul lights up his ribcage, and it is secreting a viscous substance. He reaches inside slowly and pulls out the glowing heart of essence, sighing in satisfaction as his phalanges rub against it. A slightly less intense glow begins to emanate from below him, and he knows his cock has materialized, as well as his tongue. 

With a huff, he sinks his fingers into his soul with one hand and begins to desperately rut into the pillow, squeezing it with his other hand. He throws his head back and a string blush suffuses his face as he whines in pleasure, pelvis slamming against cotton, cock throbbing. He imagines, instead of the pliable plush of the pillow, your smooth skin, your wet heat, the way you say his name so reverently. Another glow appears, from behind his eyelids, and he knows this is the part where his magic will get out of control.

His magic gathers in the air in several spots, glowing blue, and materializing into disembodied hands. They float for a moment, flexing their fingers, then swoop in towards him. Simultaneously, magic erupts from his ribcage, taking on long, coiling, solid shapes, tendrils oozing from his clavicle and sternum and out from the bottom of his ribcage. One disembodied hand is stroking his spine, one has its fingers tangled in his ribcage, and another is furiously pumping his cock. The tendrils wiggle and wrap around his soul and snake into his skull through his mouth. A few more wrap around his legs, in between his tibia and fibula. 

All the while, sans is panting, tongue hanging out as he frantically ruts against the cushion. He knows he won't ever be satisfied, unless he has you, but he also knows it would be unbearable to ignore his heat. His whole body is almost completely surrounded by magic, every bone stimulated (ba-dum tsss) and he becomes completely immersed in his own pleasure. So immersed, unfortunately, that he doesn't realize that he's been at it for literally hours. 

His heat is intense enough for him to lose track of time, and immersive enough that he doesn't hear you coming home early.


	2. with you

**Summary for the Chapter:**

> you havin fun yet or

**Notes for the Chapter:**

> here it is, thank u ladies and gentlemen *jumps into the garbage bin*

As soon as you get home, something is amiss. Usually on Saturdays, sans is lounging on the couch, napping or catching up with some reading with the television on in the background. And he always leaves the kitchen light on, even when you remind him to turn it off when he's done using it. But the living room is dark, lit only by the glow of the setting sun filtered by the semi-opaque curtains, casting an eerie light across the room. It looked as though sans hadn't been downstairs at all.

As you walk towards the staircase, you hear sans's voice echoing faintly down the hall. Is he... whining? Your first thought is that he's hurt, but... it's so lewd. Once at the top of the staircase, the strong blue glow emanating from under the door is apparent, and you become absolutely certain that your suspicions are correct. You tentatively walk towards the end of the hall, and his muffled whines and pants become louder. He sounds more agitated and loose than you've ever heard him. Usually he holds so much back...

You stop when you hear him loudly hiss your name, then moan lasciviously. You blush and put your hand to your face. He never says your name like that... hearing it fills you with determination. You boldly stride down the hall and open the bedroom door.

You're met with quite a sight. The thick curtains are drawn in the room, and since you hadn't bothered to turn on any lights in the living room or hall, the strong blue glow of his magic was striking against the darkness. sans is a mess, tendrils of electric blue whipping around, golden hands stroking every possible surface, his eye furiously fluctuating between bright blue and brighter gold... if not for the sexual nature of his predicament, one would think his magic was injured and acting out. Indeed, it seems that he has no control over any of his powers.

He turns to you, eyes wide and crazed, and gasps.

"n-nooo you can't see me like this, you weren't supposed to see this i'm sorry, shit--"

"Sans, it's okay!" you assure him, hands reaching out towards him. He flinches. A tentacle reaches up and snakes into his eyesocket. You approach him steadily, and he shrinks away. "Why don't you want me to see you like this? What even is this??"

He seems to be focusing all his available energy into self control. His eyes search your body hungrily, and he bites his tongue before speaking. "i'm in heat and it's embarrassing and I don't want to break you, i know it'll be too much and i can't control myself, just... please..." the last word comes out of his mouth in a different tone of voice, and you get the feeling that he doesn't mean 'please leave'. You bite your lip.

"Well, maybe I can help you?" A feeling of slight panic rises as you see some of the golden-blue hands reaching for you.

"don't say that, you aren't equipped to handle this, i don't want you to get hurt, please darling--"  
You cut him off by reaching forward and putting a finger on his lips. Rogue tendrils of magic wrap around your finger. Your cheeks flush with excitement as you whisper to him, "I can handle it." That was all he needed; or at least, all his magic needed, to move forward with a frenzy.

Immediately, tentacles swoop down into your clothing and more hands materialize to take the garments off. "Straight to the naughty bits I see-- aaahhh...."

A hand closes the door and several thicker blue appendages drag you by the wrists towards the bed. You run your hands down his ribcage, and he comes undone by your simple action. Immediately, he flips you to face him and throws you on your back onto the bed, grinning a feral smile. You've never seen him this animalistic, his canines gleaming in the eerie blue light. He growls low in his throat, hands pinning you down by the shoulders roughly. A hand, not his bony hand, slips between your already wet folds and rubs your clit vigourously, while another squeezes your nipple. Sans leans down and licks the crook of your neck, then bites down hard, keeping his teeth there, just weak enough to not break the skin, but hard enough that you know he'll leave a bruise. The hand leaves, and with no preperation, his cock slides into you quickly and suddenly and completely. He forces himself to hilt on the first thrust, pelvic bones slapping against your inner thighs. This was going to be a wild ride.

He thrusts into you mercilessly, setting a quick pace from the get-go. One tentacle teases your clit, and another prods at your other entrance, but doesn't enter, thankfully. A hand goes for your face, sticking its thumb betwixt your lips and stretching your mouth out to allow a particularly phallic tentacle to enter. You open your jaw, letting him fuck your face. He tastes like raspberry soda.

The stimulation is just too much; his intense magic hums with power, giving off vibrations that are driving you crazy. The appendage at your other entrace slowly begins to push its way in, stretching your tight ring of muscle. His cock is still mercilessly driving into you, and his sweet moans are infectious. Without any warning whatsoever, or even change in sans's blissed-out expression, he orgasms explosively, thick ropes of liquid magic shooting at your cervix forcefully. The pressure is so great that sans is forced back a bit, and blue, warm, viscous liquid dribbles out of your entrance. You sigh blissfully, but the look in his eye tell you that it isn't over.

You somehow find yourself on your hands and knees, then just on your knees, as your arms are held behind your back by several tentacles and you're left to brace yourself on your face. Sans enters you quickly from behind, and another tenacle, bigger this time, immediately invades your other entrance. This time, the hand at your clit is more precise with its ministratons, and the feeling of the intense magic vibrating against the sensitive nub, along with the feeling of sans's thick, swollen cock pushing and rubbing against your tight walls, and various other appendages touching you all over your body, massaging your skin, causes you to go over the edge. You cum with sans's name on your lips, back arching even further. Sans reaches with his own hand to grab your hair and pull harshly as your walls spasm and squeeze around him. With a half moan, half shout, sans cums again, but it seems even more intense, more real. You can feel your walls drawing him in, gripping onto his thick cock despite all the slippery cum. His hand squeezes in your hair, and his other hand is gripping tightly onto your thigh. You both ride out the last waves of your orgasm, and you feel the hands dissapating and the tnetacles sliding back into his ribcage, one by one, until its just his hard, bony fingers gripping onto you like a lifeline. Finally, his member slides out of you, still twitching and hard, but you can tell sans is just too tired to continue. You both collapse side by side, bodies shaking.

When you finally recover enough to move, you turn to him, questions on your tongue, but he's already asleep. You might as well clean up now. You sit up and survey the mess. It seems as though some of his magic went awry enough to knock things off of shelves, there is cum all over the walls and ceiling as well as the sheets and yourself, and sans's magic is still somewhat turbulent in his rib cage, but latent and exhausted. His soul throbs. Your legs shake as you stand up slowly, and despite the ache in your shoulders from being tied up, your neck from his strong teeth, and your scalp from his incessant pulling, you feel satisfied. You resolve to make sure you know whenever he's in heat.

**Notes for the Chapter:**

> i dunno maybe i'll write a chapter three, i mean,,,, i don't know  
> EDIT: no way in fuck im writing a chapter 3


End file.
